A Molecular Turnstile as an E‐Field‐Triggered Single‐Molecule Switch: Concept and Synthesis

A new single‐molecule switching concept relying on the E ‐field‐dependent orientation of a push‐pull system (via its dipole moment) is presented. As first steps towards realizing the E ‐field‐triggered single‐molecule motion, the synthesis of turnstile 1 , which is designed to bridge a gap within a carbon nanotube junction, is reported. Turnstile 1 consists of a hexakis( m ‐phenyleneethynylene) macrocycle decorated with phenanthrene‐functionalized oligo(phenyleneethynylene) (OPE) wires at opposite ends, as well as a para ‐connected push‐pull rod as rotator unit. The similarity of the rotor dimension with the surrounding macrocycle guarantees efficient π‐stacking between both subunits when an E ‐field is applied. To introduce a dipole moment into the rotator, the structure is terminally functionalized with a nitrile group on one side and with a dimethylamino group on the opposite end. Synthetic protocols based on Sonogashira–Hagihara couplings were developed to build up the macrocycle scaffold. The highly functionalized open precursor A is the key building block of the sequence as it allows a twofold intramolecular palladium‐catalyzed cyclization reaction to be performed to obtain the target turnstile in a very good yield of 68 %. The target structure was fully characterized by NMR spectroscopy and mass spectrometry. Furthermore, 1 H‐ 1 H NOESY NMR experiments pointed to a pseudo‐rotation of the push‐pull rod within the turnstile structure on the time scale of the NMR experiment.